DESCRIPTION

The RSA_padding_xxx_xxx() functions are called from the RSA encrypt,
decrypt, sign and verify functions. Normally they should not be called
from application programs.

However, they can also be called directly to implement padding for other
asymmetric ciphers. RSA_padding_add_PKCS1_OAEP() and
RSA_padding_check_PKCS1_OAEP() may be used in an application combined
with RSA_NO_PADDING in order to implement OAEP with an encoding
parameter.

RSA_padding_add_xxx() encodes fl bytes from f so as to fit into
tlen bytes and stores the result at to. An error occurs if fl
does not meet the size requirements of the encoding method.

The random number generator must be seeded prior to calling
RSA_padding_add_xxx().

RSA_padding_check_xxx() verifies that the fl bytes at f contain
a valid encoding for a rsa_len byte RSA key in the respective
encoding method and stores the recovered data of at most tlen bytes
(for RSA_NO_PADDING: of size tlen)
at to.

For RSA_padding_xxx_OAEP(), p points to the encoding parameter
of length pl. p may be NULL if pl is 0.

RETURN VALUES

The RSA_padding_add_xxx() functions return 1 on success, 0 on error.
The RSA_padding_check_xxx() functions return the length of the
recovered data, -1 on error. Error codes can be obtained by calling
ERR_get_error(3).